DESCRIPTION: Normal platelet production and platelet function are critical to the maintenance of vascular integrity. Abnormalities in these processes contribute to several important inherited and acquired platelet disorders such as thrombocytopenia and platelet storage pool disease (SPD). Recent studies indicate that (a) inherited thrombocytopenia due to lowered rates of platelet production is common in humans and (b) that SPD is a very common cause of inherited prolonged bleeding in humans. Current treatment of these disorders by platelet transfusions contains a risk of transmission of blood borne infectious diseases and of alloimmunization of patients. Nevertheless, knowledge of genes regulating platelet production and platelet of SPD is very limited. The specific Aims are to: 1) identify and partially characterize the gm gene by a positional cloning approach; 2) simultaneously approach the identification and partial characterization of the gm gene by a candidate gene approach; and 3)initiate studies to identify the sdy gene by a positional candidate approach. Molecular markers located within 0.3 centiMorgans (3 X 105 base and pairs) of the gm and sdy genes will be identified by comparing the segregation of each gene and microsatellite and/or CDNA markers in interspecific mouse backcrosses.